1. Technical Field
The invention relates to a liquid crystal panel, particularly, to a liquid crystal panel suitable for a driving system according to a fringe field switching (FFS) mode.
2. Background Art
A liquid crystal panel has features of lighter weight, a flat-panel and lower electric power consumption in comparison with a cathode ray tube (CRT), and therefore is used for many electronics as a display use.
According to the liquid crystal panel, orientation of liquid crystal molecules aligned in a predetermined direction is changed by an electric field to change an amount of light transmitted through a liquid crystal layer, thereby displaying an image.
The liquid crystal panel includes a reflective type in which outside light enters the liquid crystal layer to be reflected on a reflector, and reflected light re-transmits the liquid crystal layer and is emitted, a transmissive type in which incident light from a backlight apparatus transmits the liquid crystal layer, and a transflective type having both properties.
Moreover, specific methods for applying the electric field to the liquid crystal layer of the liquid crystal panel include a longitudinal electric field system and a transverse electric field system.
In the liquid crystal panel according to the longitudinal electric field system, an electric field substantially in a longitudinal direction is applied to liquid crystal molecules by means of a pair of electrodes arranged by interposing the liquid crystal layer. As the liquid crystal panel according to the longitudinal electric field system, a liquid crystal panel having a mode such as a twisted nematic (TN) mode, a vertical alignment (VA) mode and a multi-domain vertical alignment (MVA) mode is known.
In the liquid crystal panel according to the transverse electric field system, a pair of electrodes is mutually insulated and arranged on an inner surface side of one of substrates of a pair of substrates arranged by interposing the liquid crystal layer, and an electric field substantially in a transverse direction is applied to the liquid crystal molecules. As the liquid crystal panel according to the transverse electric field system, a liquid crystal panel having an in-plane switching (IPS) mode in which a pair of electrodes does not overlap in a planar view, and a fringe field switching (FFS) mode in which a pair of electrodes overlaps in the planar view are known.
The liquid crystal panel according to the transverse electric field system allows obtaining of a wide viewing angle, and therefore has been increasingly used in recent years.
Moreover, the liquid crystal panel includes a monochrome display type and a color display type.
A color of one pixel of the color display type liquid crystal panel is determined by a color mixture of light transmitted through each sub-pixel individually equipped with color filters of three primary colors including red (R), green (G) and blue (B), for example. For example, if a voltage corresponding to 0 gradations to 255 gradations of 8 bits is applied to each sub-pixel of RGB, brightness of each sub-pixel is divided into 256 kinds, and many colors can be displayed with one pixel by a combination of brightness of each of the sub-pixels.
In the liquid crystal panel formed of such sub-pixels of RGB, a white display is obtained by lighting all of the sub-pixels of RGB.
However, a manufacture error or process variation during forming an insulating film, a resin layer or the like to be formed on a substrate of the liquid crystal panel causes disruption of chromaticity and brightness of RGB, resulting in a phenomenon in which, even when a voltage of identical graduation is applied to each sub-pixel of RGB, the light is not whitened but turns to be yellowish.
As a method for solving such a problem, Patent literature No. 1 below discloses an art in which, in a transflective liquid crystal display apparatus having a reflection display unit and a transmission display unit for every pixel, an area of a light-shielding region arranged in the reflection display unit of each pixel is adjusted so as to have transmission chromaticity substantially in coincidence with reflective chromaticity in a white display, thereby adjusting an opening ratio of the reflection display unit of at least one pixel of three pixels having different coloring.
As a method for constituting a color filter, a method for dispersing an organic pigment into resin such as acryl resin is mainly applied. In the above case, a scattering degree of incident light changes depending on a state of dispersion of pigment particles, and depolarization (degree of depolarization conditions) also changes.
Accordingly, when a difference of contrast in each color of RGB is large, an amount of light leaked from each pixel is significantly different, and therefore even when color adjustment is executed based on color characteristics during the white display, a phenomenon in which a color balance is disrupted during a black display arises.
As a method for solving such a problem, Patent literature No. 2 below discloses a method in which, in a substrate of a liquid crystal display apparatus in which a pixel or a pattern of a colored layer of red, green and blue is formed on an optically transparent support, relation between contrast of each colored layer and contrast of a polarizer is optimized, thereby having high contrast and minimizing a color difference between the white display and the black display.
Furthermore, Patent literature No. 3 below discloses that, in a liquid crystal display panel according to an FFS mode, a transmittance of a sub-pixel of at least one color among sub-pixels of a plurality of colors that form one pixel is further minimized, in comparison with a transmittance of sub-pixels of other colors, without depending on a light-shielding layer, and even when a relative positional deviation of a slit-shaped opening and a light-shielding layer arises, a white balance can be properly maintained.